Process for preparing filaments from acrylonitrile polymer-containing compositions



Patented June 18, 1963 3,094,502 PROCESS FOR PREPARlNG FILAMENTS FROM ACRYLONITRILE POLYMER-CONTAINENG COMPOSITIONS John Farago, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., :1 corporation of Delaware No Drawing. Filed Dec. 2, 1959, Ser. No. 856,663 5 Claims. (Cl. 260-305) This invention relates to a novel process for the production of shaped acrylonitrile polymers and articles therefrom.

The utility of shaped articles of acrylonitrile polymers (i.e., polymers containing 80% or more acrylonitrile) is well known. conventionally, these are made by dryor wet-spinning and casting techniques. The high molecular weight polymers necessary for the preparation of shaped articles having outstanding physical properties can be used in solution concentrations up to about 22% in dryand wet-spinning operations. In the case of filament preparation, the spinning speeds are limited by the rate of evaporation of the solvents in dry-spinning and by the rate of coagulation of the polymer in a wet-spinning bath.

Many condensation polymers can be shaped into articles such as filaments, for example, at much higher rates of speed by means of melt-casting or melt-spinning techniques. The formation of shaped articles from polyacrylonitrile melts is extremely difiicult because acrylonitrile polymers cannot be melted without decomposition. The prior art has attempted to extrude plasticized melts of acrylonitrile polymers by intimately mixing powdered dry polymer with a plasticizing agent, melting the mixture and extruding the plasticized polymer. Although such processeses are very useful, they have disadvantages in some applications because of the difiiculty of preparing homogeneous mixtures of the polymer and plasticizer without excessive overheating and discoloration of the polymer. Also, any inhomogenities in the mixture leads to an excessive melt viscosity and to the development of excessive pressure in the extruding equipment. Usually it is attempted to correct this defect by use of a higher temperature, but this results in an even more discolored product. The long harsh mixing conditions required for the less soluble polymers causes degradation of the polymer and a lowering of the physical properties of the shaped articles.

It is an object of this invention to provide an improved process for the production of plasticized mixtures of acrylonitrile polymers and for the melt-spinning of shaped articles therefrom. A further object is to provide a homogeneous mixture of acrylonitrile polymer and a specific plasticizer from which shaped articles of excellent color and uniformity can be prepared.

These objects are accomplished according to this invention by intimately admixing from about 40* to about 80% by weight of an acrylonitrile-containing monomeric material with from about 60 to about 20% by weight of a plasticizer selected from the group consisting of dimethyl sulfoxide, succinonitrile, and a dimethyl sulfoxide-dimethyl sulfone mixture containing at least about 50% of the sulfoxide component; heating the mixture to a temperature between about 50 and about 130 C. in the presence of a vinyl monomer polymerization catalyst whereby the monomeric material polymerizes to an extent of at least about 60% up to about to provide a plasticized mixture containing between about 40 and about 80% of the polymerized monomeric material; removing any excess monomeric material and extruding a melt of the plasticized mixture at a temperature between about and about 180 C., preferably between about and about (3., into shaped articles, such as filaments and films. These articles are then set by quenching and the plasticizer is extracted. When filaments have been formed, they are then drawn.

By blending the monomeric material and plasticizer and then polymerizing the monomeric component a plasticized homogeneous mixture of the polymer is obtained which can be melt-spun into uniform filaments of excellent color and strength characteristics.

By the expression an acrylonitrile-containing monomeric material is meant acrylonitrile itself or a mixture of monoethylenically unsaturated monomeric materials containing at least 80% acrylonitrile plus other monomers copolymerizable therewith, such as ethylenically unsaturated sulfonic acids as methallyl sulfonic acids and others as disclosed in US. Patents 2,527,300 and 2,601,256 and other monomers as disclosed in Jacobson US. 2,436,- 926 and in Arnold U.S. 2,456,3 60.

By the expression vinyl monomer polymerization catalyst is meant the well known free radical catalysts eonventionally used in vinyl monomer polymerization processes. In this class, there are included organic azo compounds as disclosed in US. Patent 2,471,959 wherein the azo, --N=N, group is acyclic and bonded from both of the nitrogens to carbons which are aliphatic in nature and at least one of which carbons is tertiary; diacyl or diaryl peroxides, such as benzoyl peroxide, t-butyl perbenzoate, cyclohexanone peroxide, and others. They may be thermally decomposed or a redox system may be used, such as a peroxide with S0 and an oxidizable heavy metal iron, such as Fe++, or an N,N-dialkyl aniline. Salts of perdisulfuric acid are also useful in a redox system. The catalyst may be employed in a conventional manner and in an amount as will be apparent to those skilled in the art. Generally, from 0.1 to about 1% by weight of monomer is preferred.

The extruded melt must be substantially free of the volatile monomer. This can be accomplished by removing the residual monomer from a normal polymerization, as by vacuum distillation, or by conducting a post-polymerization at elevated temperatures to attain substantially 100% conversion. Post-polymerization can take place in a continuous system in the last stages, in the melter, or in the spinning head during the extrusion process. Catalysts should be selected for the post-polymerization that will survive the preliminary polymerization conditions (e.g. 50 130 C.).

In its preferred embodiment, the polymerization of this invention is conducted at a rate which provides 90% conversion of the monomer to the polymers per 30 minutes of reaction time, in order that a continuous process of polymerization and melt shaping can be employed.

Shaped articles extruded into room temperature air from a melt of this invention solidify instantly upon coming in contact with the air. It may be desirable for certain applications to quench the filaments with a directed flow 0 of air or even refrigerated air or to use a liquid cooling medium.

The pressures required to extrude melts of polymer will vary with the type of extruder, diameter, and length of extrusion orifices, the number of orifices and type of filter. However, the improved homogeneity of the polymer melts of this invention permits the use of much lower pressures and less expensive extrusion apparatus. Generally, pressures not greater than 2000 p.s.i. and usually less than 1000 p.s.i. are required in the preparation of textile yarns at an extrusion rate of 2 grams/minute per orifice.

The polymer melts contain between about 40 and about 80% polymer, preferably between about 50 and about 65%. When lower concentrations are used, the filaments tend to become tacky and stick together. When higher Concentrations are used, excessive extrusion temperatures are required, resulting in discolored yarn.

The process of this invention affords filaments with as spun deniers from 2 to 100 and higher and total yarn deniers of 80 to 80,000.

Due to the improved uniformity of the plasticized melts of this invention, higher continuous spinning speeds can be used than have been possible heretofore. For example, spinning speeds in the range of 100 to 4000 yards per minute may be used. I

Textile fibers prepared in accordance with this invention, in the form of continuous filaments or cut staple, are useful in all manner of textile application, such as in woven or knitted fabrics, carpets and the like.

The expression inherent viscosity as used in the examples is defined as:

In (n) wherein c is the concentration in grams of the polymer in 100 ml. of the solvent, (n) is the relative viscosity computed from the ratio of the flow times in a viscosimeter of polymer solution and of the solvent, and In is the logarithm to the base e. The measurements are made for solutions containing 0.5 gram per 100 ml. of solvent.

The expression intrinsic viscosity signifies the value of In (n) at the ordinate axis intercept (i.e., when 0 equals 0) in a graph of In (n),

as ordinate with 0 values as abscissas.

EXAMPLE I A continuous polymerization vessel comprising a 38" long steam heated tube with an inside diameter of 2 inches, composed of three sections of substantially equal length and containing a closely fitting metering screw driven by a 7 /2 H.P. motor with suitable coup-ling and seals, is provided.

A mixture of acrylonitrile monomer (1034 grams), methylacrylate (44 grams), sodiumallyl sulfonate (22 grams), dimethyl sulfoxide (900 grams), 1,1'-azo dicyclohexanecarbonitrile (1.08 grams, 0.1% based on total monomer weight) and alpha,alpha'-azodiisobutyronitrile (2.7 grams, 0.25% based on total monomer Weight) is placed in a stainless steel container under nitrogen pressure and connected to the above polymerization vessel, which is filled with the monomer mixture and the outlet and inlet valves closed. The first, second, and third sections of the polymerizer are heated by means of steam to 100, 130 and 150 C., respectively. After 35 minutes, the inlet and outlet inch) valves are opened, the

motor turned on, and the speed of the screw is adjusted to afford a residence time of 30 minutes for the monomer in the vessel. The product is extruded as a transparent, rough surfaced cylinder of /1. inch in diameter which solidifies to a soft, rubbery transparent gum containing 52% polymer and essentially no monomer, upon striking the air. The polymer present in the gum has an average inherent viscosity of 0.85.

The homogeneous gum is cut into A" x 4" pieces and placed in a hopper over an electrically heated (60 to C.) vertical tube (1% diameter and 12" long) containing a loosely fitted auger type revolving screw. The melted gum is fed directly downward at 25-50 p.s.i. to a spinning block containing a gear spinning pump, a 1" thick sand filter and a 2" diameter spinneret containing 20 orifices of 0.012" in diameter. The spinning block is kept at -160" C. with electrical heaters. Filaments are extruded at 800 p.s.i. to obtain filaments which solidify immediately upon striking the room temperature air below the spinneret and are wound up at 150 yards per minute (y.p.m.).

The yarn is washed in cold water to remove the dimethyl sulfoxide and is then drawn to 4 times its .as-spun length (4.0 draw ratio) in 90-95 C. water.

The resulting filaments of excellent quality are strikingly white, have a tenacity of 3.0 grams per denier (g.p.d.), a break elongation of 45%, and an initial modulus of 30 g.p.d. I

A more preferred process is to feed the molten product of the polymerizer directly to a heated reservoir and thence to a spinning pump and spinneret.

EXAMPLE II A mixture of acrylonitrile (77.5 grams), methyl acrylate (5.04 grams), dimethyl sulfoxide (67.5 grams), alpha, alpha'-azo bis( alpha,gamma-dimethylvaleronitrile) (0.165 gram, 0.2% based on monomer) and 1,1-azo dicyclohexanecarbonitrile (.083 gram, 0.1% based on total monomer weight) in a nitrogen atmosphere is polymerized in a 500 ml. resin kettle equipped with a stainless steel stirrer and a condenser cooled with Dry Ice-acet0ne. The reaction mixture is maintained at 80 C. by means of a hot water bath. After 30 minutes, the reaction mixture is a clear viscous solution containing 44% polymer (80% conversion) of inherent viscosity 1.10. The kettle is heated under a vacuum of 16 mm. at 80 C. for 5-10 minutes to remove most of the excess monomer. The solution is then poured into glass dishes where it quickly solidifies into a clear rubbery gum.

The gum (containing about 50% polymer and some monomer) from three such polymerizations is cut into pieces about A x A" and extruded as filaments using the apparatus (screw melter and extruder) and conditions of Example I.

The 400 denier (5 filaments) as-spun yarn is drawn at l0 draw ratio over a 143 C. hot plate. The drawn yarn (40 denier) has a tenacity of 5.8 g.p.d., an elongation at the break of 10.2%, and an initial modulus of 114. The yarn is strikingly white in color and bubble-free.

The more inactive catalyst 1,1'-az0 dicyclohexanecarbonitrile (half life of 23 hours at 80 C.) initiates polymerization of the residual monomer in the screw melter and extruder and thus prevents the formation of bubbles in the filaments. If desired, the monomer can be completely removed by vacuum distillation.

Similar results are obtained when the azo catalysts in the polymerization are replaced with: di-tertiary butyl peroxide, tertiary butyl per-benzoate activated with S0 and Fe++ (effective at 50 C.) or benzoyl peroxide activated with S0 and Fe++.

The use of S0 gives filaments of the highest white color and, for this reason, is preferred.

A polymer (50 parts), made in an aqueous medium, of the same composition and molecular weight as above, is mixed with dimethyl sulfoxide (50 parts) of a Banbury mixer. When it is attempted to spin the resulting sticky, opaque, non-homogenous mixture in the above apparatus it is noted that it is not .spinnable at the same temperature or even at C., at which temperature the yarn would be discolored if spinnable.

EXAMPLE III A mixture of acrylonitrile (115 grams), methyl acrylate (7.5 grams), sodium allyl sulfonate (2.5 grams), di-

methyl sulfone (50 grams), dimethyl sulfoxide (75 grams), alpha,alpha-azo bis(alpha,gamma-dimethylvaleronitrile) (0.31 grams, 0.25% based on monomer), 1,1'-azo dicyclohexanecarbonitrile (0.12 grams, 0.10% based on monomixer, no filament can be extruded at 2000 psi. using an orifice 10 mils in diameter or smaller even through the use of a lower molecular weight polymer would make the extrusion much easier.

mer), alpha,alpha'-azodiisobutyronitrile (0.12 grams, 0.10% based on monomer) is placed in the apparatus of EXAMPLE V Example II and heated to 80 C. The dimethyl sulfone A mixture of acrylonitrile (11.3 grams), methyl acrydissolves in about 2 minutes and the polymerization starts late g O e of t e p sticizers shown in Table I in about 3 minutes. At the end of 67 minutes of heating grams) and the Catalyst p p '-a o sat 80 C., the clear fluid reaction product is poured from 10 (alpha,gamma-dimethylvaleronitrile) (0.024 gram, 0.2% the flask into glass trays to harden into a clear, rubbery based on monomer) is polymerized in a 100 m1. Erlensoft gum. The conversion is 68.5% and the polymer meyer flask fitted with a condenser and a magnetic stirrer has an inherent viscosity of 1.06. The gum is cut into and heated by a water bath to 80 C. The results are pieces about A by A given in Table I.

Table I Time, Conver- Inherent Product, Remarks at Room Spinning Behavior, Item Plasticizer Minutes sion, Viscosity Temperature Remarks Percent Dimethyl sulioxide 49 1. 45 Clear, uniform rubbery gun-- Excellent. Dimethyl sultoxide/di- 22 35 1. 47 Clear, uniform soft, rubbery Do.

methyl sulfone 50/50. um. Succinonitrile 12.5 45 1.2 Clear, uniform gum- Good. Dimethylacetamide 17 27 0- 74 White, Wax Not spinnable-to 0 weak to wind up. Dimethylformamide 15 Less thaln) Precipitate of polymer Not spinnable. Tetramethylene sulfone..- 27 20 1.54 Thick,waxlike liquid Poor-maxirnu1n spinning speed 100 y.p.m., frequent breaks; yellou color. 7 Ethylene carbonate 10 26- 9 1. 33 White soft paste Poor (spinning speeds less than 80 y.p.m., required); yellow color.

1 43% plasticizer, all others 40%.

The pieces of gum are placed in a hop-per located above 35 In all cases, except when using the dimethyl sulfoxide, the entrance to a screw extruder comprising a 12" long succinonitrile or dimethyl sulfoxide dimethyl sulfone mix- (1" inside diameter) stainless steel barrel containing a tures of this invention, unsatisfactory results are obtained, closely fitting stock screw coupled to a motor with suit such as low conversion of polymer or production of low able seals which feeds an electrically heated elbow block molecular weight polymer. mounting, a filter pack, and a S-hole (10 mil diameter) The results obtained when attempting to spin the prodspinneret for the vertical extrusion of filaments. The ucts at 1000 p.s.i. and 180 C. (after removal of residual first section of the extruder is cooled with cold water, the monomer and sufficient plasticizer to give a gum consecond section is heated to 150 C., the third section and taining about 40% solids) in a simple press spinner are connecting elbow are heated to 170 C. Excellent spinalso shown. A spinning temperature of 185 C. was ning is obtained with no excessive buildup of pressure required for items 6 and 7, but still the results are poor. (less than 1500 p.s.i.) and the yarn is wound up continu- It has also been noted that the presence of an acid or ously at 250 y.p.m. The as-spun yarn is washed in cold a base (e.g., an acid modified polymer) in a plasticized water to remove the plasticizers and is then drawn 8 X melt containing a cyclic ester such as butyrolaetone or through a tube containing steam at atmospheric pressure. ethylene carbonate causes degradation of the plasticizer The drawn yarn (1.9 d.p.f.) has a tenacity of 1.9 g.p.d. and the formation of bubbles of gas in the melt in pressed and is very uniform and of a good white color. films or extruded filaments when temperatures in excess Mixtures of dimethyl sulfoxide and dimethyl sulfone of 140 C. are used. containing at least 50% of the sulfoxide are satisfactory. I claim:

EXAMPLE Iv St a process for preparing a filamentary article, the

A mixture of acry g succifiofli'il'ile '(a) intimately admixing from about 40% to about grams) and The catalyst P 'P 80% by weight of a monomeric material consisting (alphasamma-dimethylvaleronitrile) am 0. of at least 80% acrylonitrile and up to 20% of a based 1 monomer) is polymerized at ill PP copolymerizable monoethylenically unsaturated monratus of Example III. After 2 minutes, the clear fluid Omar ith f o b t 60% 1 b t 20% by weight Product is Poured Onto a glass Plate whereupon i i m of a plasticizer selected from the group consisting of ately solidifies to a rubbery, transparent, homogeneous- :(1) .dimethylsul-foxjde, (2) gi it fl (3 a i appearing A conversion is Obtained and ture of dimethylsulfoxide and dimethylsulfone conthe polymer has an inherent viscosity of 3.42. Essentially taming t le t b t 50% b volume f dimethylall of the residual monomer is removed under vacuum. sulfoxide,

The gum is cut into /4. particles and spun from a press adding a vinyl monomer polymerization catalyst Spinner consisting of an electrically heated u to the mixture of monomeric material and plasticizer C.) of 1" inside diameter containing a hydraulically in an o t b t e ab t 0.1% d ab t 1 0% driven piston at one end and a sand pack filter and spinby Weight f id monomeric t i l,

neret (5 holes of .010 in diameter) heated to 170180 70 (c) heating the resulting mixture to between about C. at a pressure of less than 1000 p.s.i. and the White 50 C. and about 130 C. to polymerize said mono filaments wound up at 100 y.p.m. meric material to an extent of at least about 60% When the above gum is replaced with composition 013- to provide a plasticized mixture containing from tained by mixing polyacrylonitrile (inherent viscosity 1.1) about 40% to about 80% by weight of polymerized with succinonitrile in a Waring Blendor or a Banbury 75 monomeric mixture,

/ 8 (d) substantially removing residual volatile monomer, The novel process of claim 1 wherein the mixture and is extruded into the form of filaments. f(e) melt-extruding the plasticized material at a temperature between about 120 C. and about 180 C. References Cited in the file of this patent to form a filamentary article. 5 V 2. The novel process of claim 1 wherein: the plasticizer UNITED STA YES PATENTS s 3 g y s sqq u the catalyst lwnslsts of 2,404,717 Houtz J l 23, 1946 0 exanecar W o 2,456,360 Arnold Dec. 14, 1948 I v e novel process of claim 1 wherein the convers1on 2 776 946 L tt t 1 I 8 1957 rate of the monomer to the polymer is at least about 90% 10 2779746 on e a per minutes of Ramon He1senberg et al. July 29, 1957 2,858,288 Ehlers et a1 Oct. 28, 1958 4. The novel process of claim 1 wherein the extrusion temperature is between about and about C. 

1. IN A PROCESS ADMIXING FROM ABOUT 40% TO ABOUT STEPS OF (A) INTIMATELY ADMIXING FROM ABOUT 40% TO ABOUT 80% BY WEIGHT OF A MONOMERIC MATERIAL CONSISTING OF AT LEAST 80% ACRYLONITRILE AND UP TO 20% OF A COPOLYMERIZABLE MONOETHYLENICALLY UNSATURATES MONOMER WITH FROM ABOUT 60% TO ABOUT 20% BY WEIGHT OF A PLASTICIZER SELECTED FROM THE GROUP CONSISTING OF (1) DIMETHYLSULFOXIDE, (2) SUCCINONITRILE, (3) A MIXTURE OF DIMETHYLSULFOXIDE AND DIMETHYSULFONE CONTAINING AT LEAST ABOUT 50% BY VOLUME OF DIMETHYLSULFOXIDE, (B) ADDING A VINYL MONOMER POLYMERIZATION CATALYST TO THE MIXTURE OF MONOMERIC MATERIAL AND PLASTICIZER IN AN AMOUNT BETWEEN ABOUT 0.1% AND ABOUT 1.0% BY WEIGHT OF SAID MONOMERIC MATERIAL, (C) HEATING THE RESULTING MIXTURE TO BETWEEN ABOUT 50*C. AND ABOUT 130*C. TO POLYMERIZE SAID MONOMERIC MATERIAL TO AN EXTENT OF AT LEAST ABOUT 60% TO PROVIDE A PLASTICIZED MIXTURE CONTAINING FROM ABOUT 40% TO ABOUT 80% BY WEIGHT OF POLYMERIZED MONOMERIC MIXTURE, (D) SUBSTANTIALLY REMOVING RESIDUAL VOLATILE MONOMER, AND (E) MELT-EXTRUDING THE PLASTICIZED MATERIAL AT A TEMPERATURE BETWEEN ABOUT 120*C. AND ABOUT 180*C. TO FORM A FILAMENTARY ARTICLE. 